1. Field of the Invention
This invention is in the field of safety devices; more particularly, this invention is directed to the field of devices to prevent injury to workers in situations where there is a danger of falling.
2. Description of the Prior Art
Wherever workers perform duties in unenclosed surroundings substantially above a base level, there is a danger of the worker falling from the work station and being injured or killed. Situations of this nature could occur, for instance, in the construction of tall buildings, within existing structures, inside subterranean operations such as salt or coal mines, or on residential structures. There are even standard statistical figures for the expected number of deaths, most frequently due to falls from the structure, for building and bridge construction.
Despite statistics, any loss of human life is clearly unacceptable where it can be prevented. In the past, the methods used for worker safety have up to now been either expensive, cumbersome or only marginally effective, and sometimes all of these simultaneously. Some examples are the use of wooden snow fence on the sides of unclosed high-rise construction; safety nets at or below the sides of open work areas; static safety lines attached to the worker and to the work structure; and various other forms of physical barricades.
While a wooden fence is effective, it is not completely fail-safe, and there is the possibility that a worker could either fall over the top thereof or break through the fence at a point of attachment. Further, there are times and places where a fence cannot be used due to construction peculiarities, such as when the side or edge of a building floor is itself the subject of the construction effort. In such a case, a safety net, maintained below the work area, is the usual alternative.
The safety net is of significant value in worker safety, and has proven its effectiveness both in keeping the worker safe in the event of a fall, and in not subjecting him to associated problems involved in the operation of the net itself; in other words, the worker falling into a net is not likely to suffer injury caused by the net, where he might still have a few bruises from a wooden fence, or internal injuries from a safety line. The cost of safety nets however, is substantial; the labor involved is a significant and non-productive, though necessary, cost in the construction process. Further, the process of rigging the net itself is hazardous to a degree.
The static safety line, in terms of cost and time, is the most effective of the safety devices used in keeping workers from injury in high-rise construction, but there are some drawbacks to its use, although none of them is serious. The most common problem is that of fouling the line; the worker must maintain constant alertness to prevent both himself and others from tripping over the line, or getting it caught in material or equipment on the job. A second problem is that when the line serves its preventive function by stopping a worker from falling, it is only after the worker has already fallen as far as the line extends; at that point, the line snaps taut, and the worker is stopped with a severe shock, one which is sufficient to cause some internal injury.
Devices are known for controlling or diminishing the rate of passage of a rope or other line. For instance, Vescovi shows devices in U.S. Pat. Nos. 1,352,230 and 1,444,015 which are useful as fire escapes. Riches, U.S. Pat. No. 737,145 and Meaders, U.S. Pat. No. 797,903, also show fire-escape devices. In all of these mechanisms, however, there is no provision for a rate-responsive action within the device; they all require the agency of the operator to control the rate of passage of the line.
While Vescovi U.S. Pat. No. 1,352,230 and Riches and Meaders all show what may be considered to be braking means, they all require human agency to set that braking means at a rate appropriate for the circumstances. There is no provision in any of these devices to permit the line to run free at a low rate while preventing its running out rapidly, unless the operator affirmatively makes that adjustment for each circumstance encountered.
Watts shows a safety brake in U.S. Pat. No. 3,830,346, useful for scaffolding. The Watts device has utility only when operating in a substantially vertical mode; and when the device is triggered by high-rate passage of the line through it, the mechanism must be disassembled before it can be made to function again.